Focusing systems and methods for use in a cochlear implant system

ABSTRACT

An exemplary sound processor ( 104 ) may 1) identify a stimulation site within a cochlea of a patient that is to be stimulated in order to represent an audio signal presented to the patient, 2) dynamically designate, based on the identified stimulation site, a first group of one or more electrodes as a group of one or more main electrodes and a second group of one or more electrodes as a group of one or more compensating electrodes and 3) dynamically determine, based on the identified stimulation site, an amount of main current to be applied to each electrode included in the first group of one or more electrodes in order to represent the audio signal and an amount of compensating current to be applied to each electrode included in the second group of one or more electrodes to focus an excitation field created by the main current.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/737,676, filed Dec. 14, 2012, the contents of whichare hereby incorporated by reference in their entirety.

BACKGROUND INFORMATION

Current steering is often used in cochlear implant systems to moreeffectively represent sound presented to cochlear implant patients. Intraditional current steering strategies, weighted stimulation current isapplied concurrently to two adjacent electrodes by a cochlear implantsystem in order to stimulate a stimulation site located in between areasassociated with the electrodes. In this manner, the cochlear implantsystem may create a perception of a frequency in between the frequenciesassociated with the electrodes.

While current steering is effective in augmenting sound perception, itmay introduce spectral broadening, which in turn may compromise spectralresolution. This may be particularly problematic in cases where an audiosignal (e.g., speech) includes spectral peaks that represent thedistinguishing or meaningful frequency components of the audio signal.In these cases, it may be desirable to present electrical stimulationrepresentative of the spectral peaks to a cochlear implant patient in asfine of spectral resolution as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments and are a partof the specification. The illustrated embodiments are merely examplesand do not limit the scope of the disclosure. Throughout the drawings,identical or similar reference numbers designate identical or similarelements.

FIG. 1 illustrates an exemplary cochlear implant system according toprinciples described herein.

FIG. 2 illustrates a schematic structure of the human cochlea accordingto principles described herein.

FIG. 3 illustrates exemplary components of a sound processor accordingto principles described herein.

FIG. 4 shows an exemplary frequency domain representation of an audiosignal that may be presented to a cochlear implant patient according toprinciples described herein.

FIG. 5 shows an exemplary analysis channel according to principlesdescribed herein.

FIGS. 6-12 illustrate various stimulation strategies according toprinciples described herein.

FIG. 13 illustrates an exemplary implementation of current steeringaccording to principles described herein.

FIG. 14 illustrates an exemplary implementation of current steering thatmay be used to dynamically focus one or more excitation fields producedby current steering electrodes according to principles described herein.

FIG. 15 illustrates an exemplary focusing method according to principlesdescribed herein.

DETAILED DESCRIPTION

Focusing systems and methods for use in a cochlear implant system aredescribed herein. As will be described below, a sound processor includedin a cochlear implant system may 1) identify a stimulation site within acochlea of a patient that is to be stimulated in order to represent anaudio signal presented to the patient, the stimulation site includedwithin a plurality of stimulation sites associated with a stimulationchannel corresponding to a plurality of electrodes, 2) dynamicallydesignate, based on the identified stimulation site, a first group ofone or more electrodes included in the plurality of electrodes as agroup of one or more main electrodes and a second group of one or moreelectrodes included in the plurality of electrodes as a group of one ormore compensating electrodes, and 3) dynamically determine, based on theidentified stimulation site, an amount of main current to be applied toeach electrode included in the first group of one or more electrodes inorder to represent the audio signal and an amount of compensatingcurrent to be applied to each electrode included in the second group ofone or more electrodes to focus an excitation field created by the maincurrent. The sound processor may then direct a cochlear implantassociated with the patient to stimulate the identified stimulation siteby applying the determined amount of main current to the first group ofone or more electrodes and applying the determined amount ofcompensation current to the second group of one or more electrodes.

As used herein, a stimulation strategy that includes “focusing” refersto a stimulation strategy that directs a cochlear implant to applycompensating current to one or more compensating electrodes while maincurrent representative of a portion of an audio signal is applied to oneor more main electrodes. As will be described below, the compensatingcurrent is opposite in phase compared to the main current and serves tofocus (e.g., narrow) the excitation field produced by the main current,thereby resulting in finer spectral resolution compared to stimulationstrategies in which focusing is not used. Focusing may also be referredto as “spectral focusing.”

By using the identified stimulation site to both dynamically designatedifferent electrodes associated with the same stimulation channel aseither main electrodes or compensating electrodes and to dynamicallydetermine different amounts of main current and compensating current tobe applied to the electrodes, the systems and methods described hereinmay enhance frequency resolution, reduce spectral smearing, and improvepatient perception of audio signals. Another benefit of the systems andmethods described herein is that they may be used to maintain a constantexcitation field width for a particular stimulation channel, which mayimprove patient perception of audio signals and minimize fluctuations innoise perception by a patient. Maintaining a constant excitation fieldwidth is described more fully in co-pending PCT Application No. ______,attorney docket number 3021-0398-WO, entitled “Systems and Methods forControlling a Width of an Excitation Field Created by Current Applied bya Cochlear Implant System,” filed the same day as the presentapplication and incorporated herein by reference in its entirety.

FIG. 1 illustrates an exemplary cochlear implant system 100. As shown,cochlear implant system 100 may include various components configured tobe located external to a patient including, but not limited to, amicrophone 102, a sound processor 104, and a headpiece 106. Cochlearimplant system 100 may further include various components configured tobe implanted within the patient including, but not limited to, acochlear implant 108 and a lead 110 (also referred to as an electrodearray) with a plurality of electrodes 112 disposed thereon. As will bedescribed in more detail below, additional or alternative components maybe included within cochlear implant system 100 as may serve a particularimplementation. The components shown in FIG. 1 will now be described inmore detail.

Microphone 102 may be configured to detect audio signals presented tothe patient. Microphone 102 may be implemented in any suitable manner.For example, microphone 102 may include a microphone that is configuredto be placed within the concha of the ear near the entrance to the earcanal, such as a T-MIC™ microphone from Advanced Bionics. Such amicrophone may be held within the concha of the ear near the entrance ofthe ear canal by a boom or stalk that is attached to an ear hookconfigured to be selectively attached to sound processor 104.Additionally or alternatively, microphone 102 may be implemented by oneor more microphones disposed within headpiece 106, one or moremicrophones disposed within sound processor 104, one or morebeam-forming microphones, and/or any other suitable microphone as mayserve a particular implementation.

Sound processor 104 (i.e., one or more components included within soundprocessor 104) may be configured to direct cochlear implant 108 togenerate and apply electrical stimulation (also referred to herein as“stimulation current”) representative of one or more audio signals(e.g., one or more audio signals detected by microphone 102, input byway of an auxiliary audio input port, etc.) to one or more stimulationsites associated with an auditory pathway (e.g., the auditory nerve) ofthe patient. Exemplary stimulation sites include, but are not limitedto, one or more locations within the cochlea, the cochlear nucleus, theinferior colliculus, and/or any other nuclei in the auditory pathway. Tothis end, sound processor 104 may process the one or more audio signalsin accordance with a selected sound processing strategy or program togenerate appropriate stimulation parameters for controlling cochlearimplant 108. Sound processor 104 may include or be implemented by abehind-the-ear (“BTE”) unit, a body worn device, and/or any other soundprocessing unit as may serve a particular implementation. For example,sound processor 104 may be implemented by an electro-acousticstimulation (“EAS”) sound processor included in an EAS system configuredto provide electrical and acoustic stimulation to a patient.

In some examples, sound processor 104 may wirelessly transmitstimulation parameters (e.g., in the form of data words included in aforward telemetry sequence) and/or power signals to cochlear implant 108by way of a wireless communication link 114 between headpiece 106 andcochlear implant 108. It will be understood that communication link 114may include a bi-directional communication link and/or one or morededicated uni-directional communication links.

Headpiece 106 may be communicatively coupled to sound processor 104 andmay include an external antenna (e.g., a coil and/or one or morewireless communication components) configured to facilitate selectivewireless coupling of sound processor 104 to cochlear implant 108.Headpiece 106 may additionally or alternatively be used to selectivelyand wirelessly couple any other external device to cochlear implant 108.To this end, headpiece 106 may be configured to be affixed to thepatient's head and positioned such that the external antenna housedwithin headpiece 106 is communicatively coupled to a correspondingimplantable antenna (which may also be implemented by a coil and/or oneor more wireless communication components) included within or otherwiseassociated with cochlear implant 108. In this manner, stimulationparameters and/or power signals may be wirelessly transmitted betweensound processor 104 and cochlear implant 108 via a communication link114 (which may include a bi-directional communication link and/or one ormore dedicated uni-directional communication links as may serve aparticular implementation).

Cochlear implant 108 may include any type of implantable stimulator thatmay be used in association with the systems and methods describedherein. For example, cochlear implant 108 may be implemented by animplantable cochlear stimulator. In some alternative implementations,cochlear implant 108 may include a brainstem implant and/or any othertype of active implant or auditory prosthesis that may be implantedwithin a patient and configured to apply stimulation to one or morestimulation sites located along an auditory pathway of a patient.

In some examples, cochlear implant 108 may be configured to generateelectrical stimulation representative of an audio signal processed bysound processor 104 (e.g., an audio signal detected by microphone 102)in accordance with one or more stimulation parameters transmittedthereto by sound processor 104. Cochlear implant 108 may be furtherconfigured to apply the electrical stimulation to one or morestimulation sites within the patient via one or more electrodes 112disposed along lead 110 (e.g., by way of one or more stimulationchannels formed by electrodes 112). In some examples, cochlear implant108 may include a plurality of independent current sources eachassociated with a channel defined by one or more of electrodes 112. Inthis manner, different stimulation current levels may be applied tomultiple stimulation sites simultaneously (also referred to as“concurrently”) by way of multiple electrodes 112.

FIG. 2 illustrates a schematic structure of the human cochlea 200 intowhich lead 110 may be inserted. As shown in FIG. 2, the cochlea 200 isin the shape of a spiral beginning at a base 202 and ending at an apex204. Within the cochlea 200 resides auditory nerve tissue 206, which isdenoted by Xs in FIG. 2. The auditory nerve tissue 206 is organizedwithin the cochlea 200 in a tonotopic manner. Relatively low frequenciesare encoded at or near the apex 204 of the cochlea 200 (referred to asan “apical region”) while relatively high frequencies are encoded at ornear the base 202 (referred to as a “basal region”). Hence, eachlocation along the length of the cochlea 200 corresponds to a differentperceived frequency. Cochlear implant system 100 may therefore beconfigured to apply electrical stimulation to different locations withinthe cochlea 200 (e.g., different locations along the auditory nervetissue 206) to provide a sensation of hearing.

FIG. 3 illustrates exemplary components of sound processor 104. It willbe recognized that the components shown in FIG. 3 are merelyrepresentative of the many different components that may be included insound processor 104 and that sound processor 104 may include additionalor alternative components as may serve a particular implementation.

As shown in FIG. 3, sound processor 104 may include a processingfacility 302, a stimulation management facility 304, and a storagefacility 306, which may be in communication with one another using anysuitable communication technologies. Storage facility 306 may beconfigured to maintain processing data 308 generated and/or used byprocessing facility 302, and stimulation data 310 (e.g., datarepresentative of one or more stimulation parameters) generated and/orused by stimulation management facility 304. Storage facility 306 maymaintain additional or alternative data as may serve a particularimplementation. One or more of facilities 302-306 may include acomputing device or processor configured to perform one or more of thefunctions described herein. Facilities 302-306 will now be described inmore detail.

Processing facility 302 may be configured to process an audio signalpresented to a cochlear implant patient (e.g., an audio signal detectedby microphone 102, an audio signal input by way of an auxiliary audioinput port, etc.). For example, processing facility 302 may perform oneor more pre-processing operations, spectral analysis operations, noisereduction operations, mapping operations, and/or any other types ofsignal processing operations on a detected audio signal as may serve aparticular application.

In some examples, processing facility 302 may divide an audio signalpresented to a cochlear implant patient into a plurality of analysischannels each containing a frequency domain signal (or simply “signal”)representative of a distinct frequency portion of the audio signal. Thismay be performed in any suitable manner. For example, processingfacility 302 may be implemented by a plurality of band-pass filtersconfigured to divide the audio signal into a plurality of frequencychannels or bands. Additionally or alternatively, processing facility302 may be configured to convert the audio signal from a time domaininto a frequency domain and then divide the resulting frequency binsinto the plurality of analysis channels. To this end, processingfacility 302 may include one or more components configured to apply aDiscrete Fourier Transform (e.g., a Fast Fourier Transform (“FFT”)) tothe audio signal.

To illustrate, FIG. 4 shows an exemplary frequency domain representationof an audio signal 402 that may be presented to a cochlear implantpatient. As illustrated by the dashed vertical lines, processingfacility 302 has divided the audio signal 402 into a plurality ofanalysis channels 404-1 through 404-7 (collectively “analysis channels404”). Each analysis channel 404 corresponds to a particular frequencyband. For example, analysis channel 404-1 corresponds to a frequencyband defined by frequencies f₀ and f₁. While seven analysis channels 404are shown in FIG. 4, it will be recognized that processing facility 302may divide the audio signal 402 into any number of analysis channels asmay serve a particular application.

Each analysis channel 404 may contain a frequency domain signalrepresentative of a distinct frequency portion of audio signal 402. Forexample, the portion of audio signal 402 that is included in thefrequency band defined by frequencies f₀ and f₁ may be referred to asthe frequency domain signal contained within analysis channel 404-1.

As illustrated in FIG. 4, various spectral peaks 406 (e.g., spectralpeaks 406-1 through 406-3) may be located within one or more of analysischannels 404. These spectral peaks 406 may represent the distinguishingor meaningful frequency components of audio signal 402. For example, ifaudio signal 402 includes speech, spectral peaks 406 may berepresentative of formants included in the speech. As used herein, aformant represents a resonance of the human vocal tract and isassociated with the utterance of a vowel sound.

Each analysis channel 404 may correspond to a stimulation channel 408(e.g., stimulation channels 408-1 through 408-7). Each stimulationchannel 408 may be defined by one or more electrodes (e.g., one or moreof electrodes E1 through E8). In the particular example of FIG. 4, eachstimulation channel 408 is defined by two electrodes. For example,stimulation channel 408-1, which corresponds to analysis channel 404-1,is defined by electrodes E1 and E2. Likewise, stimulation channel 408-2,which corresponds to analysis channel 404-2, is defined by electrodes E2and E3. While FIG. 4 shows a one-to-one mapping of analysis channels 404to stimulation channels 408, it will be recognized that multipleanalysis channels may be mapped to a single stimulation channel as mayserve a particular implementation.

Each electrode may be located at a position within the cochlea (or anyother structure within the patient) that corresponds to a stimulationsite associated with a particular frequency. For example, electrode E1is located at a position that corresponds to a stimulation siteassociated with frequency f₀. Hence, stimulation of electrode E1 byitself may result in the patient perceiving frequency f₀. As will bedescribed below, to represent an audio signal having a frequency thatcorresponds to a stimulation site located in between stimulation sitesassociated with two electrodes, current steering between the twoelectrodes may be used. It will be recognized, however, that thecorrespondence between the electrode location and the associatedspectral region may not be exact, but could depend on, among otherfactors, electrode placement and unique anatomical features of anindividual patient.

As mentioned, each stimulation channel 408 may be defined by one or moreelectrodes. However, any number of electrodes may correspond to thestimulation channel 408. For example, electrodes E2 and E3 definestimulation channel 408-2 shown in FIG. 4. However, electrodes E1through E4 may correspond to stimulation channel 408-2 in that maincurrent may be applied to one or more of electrodes E1 through E4 torepresent an audio signal (e.g., a spectral peak) included in analysischannel 404-2 and in that compensating current may be applied to one ormore of electrodes E1 through E4 to focus an excitation field producedby the main current.

To illustrate, FIG. 5 shows an exemplary analysis channel 502 thatcontains a frequency domain signal 504. In the example of FIG. 5,analysis channel 502 corresponds to a stimulation channel 506corresponding to four electrodes—electrodes E_(k−2), E_(k−1), E_(k), andE_(k+1). In this configuration, current steering between electrodesE_(k−1) and E_(k) may be used to represent frequency domain signal 504.

For example, FIG. 5 shows that main current 508-1 having a weightedamplitude of w and main current 508-2 having a weighted amplitude of 1−ware concurrently applied to electrodes E_(k−1) and E_(k), respectively.This results in a peak envelope located at frequency f. In the absenceof focusing (i.e., if no compensating current is applied to one or moreelectrodes surrounding electrodes E_(k−1) and E_(k)), the excitationfield associated with the peak envelope is relatively broad, asrepresented by envelope 510.

However, in accordance with a stimulation strategy that includesfocusing, compensating current 512-1 and 512-2 (collectively“compensating current 512”) opposite in polarity compared to that ofmain current 508-1 and 508-2 (collectively “main current 508”) may beapplied to electrodes E_(k−2) and E_(k+1) concurrently with theapplication of main current 508-1 and 508-2 to electrodes E_(k−1) andE_(k). As shown, electrodes E_(k−2) and E_(k+1) surround electrodesE_(k−1) and E_(k). Compensating current 512 serves to focus theexcitation field associated with the peak envelope, as represented byenvelope 514. It will be recognized that compensating current may beapplied by way of any number of compensating electrodes.

As will be described below, the systems and methods described hereinfacilitate dynamic selection of which electrodes are to be designated asmain electrodes and which electrodes are to be designated ascompensating electrodes. The systems and methods described herein alsofacilitate dynamic determination of an amount of main current to beapplied to each of the designated main electrodes and amount ofcompensating current to be applied to each of the compensatingelectrodes. For example, with respect to the example provided in FIG. 5,a different audio signal having a frequency domain signal included inanalysis channel 502 may be subsequently presented to the patient. Torepresent this audio signal, main current may be applied to electrodeE_(k−1) and compensating current may be applied to electrodes E_(k−2),E_(k), and E_(k+1). The dynamic designation and determination may bebased on the particular stimulation site that is to be stimulated inorder to represent the audio signal to the patient.

To this end, processing facility 302 may identify a stimulation sitewithin a cochlea of a patient that is to be stimulated in order torepresent an audio signal presented to the patient. The stimulation sitemay be included within a plurality of stimulation sites associated witha stimulation channel corresponding to a plurality of electrodes. Forexample, referring to FIG. 4, the identified stimulation site may beincluded within a plurality of stimulation sites associated withstimulation channel 408-2. To illustrate, the stimulation site maycorrespond to a first edge of stimulation channel 408-2 (i.e., belocated at a position directly stimulated by electrode E2), a middle ofstimulation channel 408-2 (i.e., be located at a position in betweenlocations directly stimulated by electrodes E2 and E3), or a second edgeof stimulation channel 408-2 (i.e., be located at a position directlystimulated by electrode E3). It will be recognized that any number ofstimulation sites may be associated with a stimulation channel.

Processing facility 302 may identify a stimulation site within a cochleaof a patient that is to be stimulated in order to represent an audiosignal presented to the patient in any suitable manner. For example,processing facility 302 may determine a frequency of a spectral peakassociated with the audio signal and included in an analysis channelthat corresponds to the frequency channel. Processing facility 302 maythen identify a stimulation site that corresponds to the identifiedfrequency. For example, in order to represent the frequency domainsignal included in analysis channel 404-1, processing facility 302 maydetermine a frequency of spectral peak 406-1 and identify a stimulationsite that corresponds to the frequency of spectral peak 406-1.Alternatively, a stimulation site may be determined after psychophysicalmasking principles are applied to determine the shape of the spectrum asit would be presented in the auditory system of a normally-hearingindividual.

Stimulation management facility 304 may be configured to manage (e.g.,control) stimulation provided by cochlear implant 108. For example, asmentioned, processing facility 302 may identify a stimulation site thatis to be stimulated in order to represent an audio signal presented tothe patient and that is associated with a stimulation channel thatcorresponds to a plurality of electrodes. In response, stimulationmanagement facility 304 may dynamically designate, based on theidentified stimulation site, a first group of one or more electrodesincluded in the plurality of electrodes as a group of one or more mainelectrodes and a second group of one or more electrodes included in theplurality of electrodes as a group of one or more compensatingelectrodes. In some examples, the first and second groups of one or moreelectrodes do not overlap (i.e., they each include a distinct set ofelectrodes). Stimulation management facility 304 may also dynamicallydetermine, based on the identified stimulation site, an amount of maincurrent to be applied to each electrode included in the first group ofone or more electrodes in order to represent the audio signal and anamount of compensating current to be applied to each electrode includedin the second group of one or more electrodes to focus an excitationfield created by the main current. Stimulation management facility 304may then direct cochlear implant 108 to stimulate the identifiedstimulation site by concurrently applying the determined amount of maincurrent to the first group of one or more electrodes and the determinedamount of compensation current to the second group of one or moreelectrodes. Various examples of this will now be provided.

In some examples, four electrodes correspond to the stimulation channelassociated with the identified stimulation site—a first electrode, asecond electrode, a third electrode, and a fourth electrode sequentiallydisposed within the cochlea. The first electrode is the most apicallydisposed of the four electrodes and the fourth electrode is the mostbasally disposed of the four electrodes. In these examples, stimulationmanagement facility 304 may perform the dynamic designation and thedynamic determination in accordance with a quadripolar with correctionstimulation strategy. As used herein, a “quadripolar with correctionstimulation strategy” is one in which stimulation management facility304 dynamically designates, based on the identified stimulation site,one or both of the middle electrodes (i.e., the second and/or thirdelectrodes) as main electrodes and the remaining electrodes ascompensating electrodes.

To illustrate an exemplary quadripolar with correction stimulationstrategy, reference is made to FIG. 6. For the sake of comparison, FIG.6 includes three panels 602-1 through 602-3 that each show excitationfields that may occur in response to stimulation of variousconfigurations of four electrodes labeled E1 through E4. In particular,panel 602-1 shows excitation fields that may occur in response tostimulation of various electrode configurations in accordance with amonopolar stimulation strategy, panel 602-2 shows excitation fields thatmay occur in response to stimulation of various electrode configurationsin accordance with a quadripolar stimulation strategy, and panel 602-3shows excitation fields that may occur in response to stimulation ofvarious electrode configurations in accordance with a quadripolar withcorrection stimulation strategy. As will be described below, thequadripolar with correction stimulation strategy may allow for a fullcontinuum of pitches between the stimulation site associated with E2 andthe stimulation site associated with E3 while at the same time focusingthe excitation fields produced by the stimulation.

Panel 602-1 shows an exemplary excitation field 604-1 (represented by adotted line) that may result in response to monopolar stimulation ofelectrode E2 in isolation. Such monopolar stimulation is illustrated inFIG. 7A. As shown in FIG. 7A, main current 702 is applied to electrodeE2 while no current is applied to electrodes E1, E3, and E4. As shown inFIG. 6, the resulting excitation field 604-1 has a peak 606-1 thatcorresponds to the stimulation site associated with electrode E2.However, excitation field 604-1 is spread broadly across a relativelylarge area, which may result in interference with adjacent stimulationchannels.

Panel 602-1 also shows an exemplary excitation field 604-2 (representedby a dashed line) that may result in response to monopolar stimulationof electrode E3 in isolation. Such monopolar stimulation is illustratedin FIG. 7B. As shown in FIG. 7B, main current 704 is applied toelectrode E3 while no current is applied to electrodes E1, E2, and E4.As shown in FIG. 6, the resulting excitation field 604-2 has a peak606-2 that corresponds to the stimulation site associated with electrodeE3. However, excitation field 604-2 is also spread broadly across arelatively large area, which may result in interference with adjacentstimulation channels.

Panel 602-1 also shows an exemplary excitation field 604-3 (representedby a solid line) that may result in response to concurrent monopolarstimulation of electrodes E2 and E3. Such monopolar stimulation isillustrated in FIG. 7C. As shown in FIG. 7C, main current 706-1 and706-2 is applied in a current steering manner to electrodes E2 and E3while no current is applied to electrodes E1 and E4. As shown in FIG. 6,the resulting excitation field 604-3 has a peak 606-3 that correspondsto a stimulation site located midway (labeled “Mid” in FIG. 6) inbetween the stimulation sites associated with electrodes E2 and E3.However, excitation field 604-3 is also spread broadly across arelatively large area, which may result in interference with adjacentstimulation channels.

As mentioned, panel 602-2 shows excitation fields that may occur inresponse to stimulation of various electrode configurations inaccordance with a quadripolar stimulation strategy. As used herein, aquadripolar stimulation strategy is one in which fixed (i.e., fixedamplitude) compensating current is applied to two electrodes surroundingtwo electrodes that define a stimulation channel. In the example of FIG.6, the stimulation channel is defined by electrodes E2 and E3 and thefixed compensating current is applied to electrodes E1 and E4.

To illustrate, panel 602-2 shows an exemplary excitation field 608-1(represented by a dotted line) that may result in response tostimulation of electrode E2 in the presence of fixed compensatingcurrent applied to electrodes E1 and E4. Such stimulation is illustratedin FIG. 8A. As shown in FIG. 8A, main current 802 is applied toelectrode E2 at the same time that fixed compensating current 804-1 and804-2 opposite in polarity compared to main current 802 is applied toelectrodes E1 and E4. No current is applied to electrode E3. Althoughthe resulting excitation field 608-1 is focused due to the presence ofcompensating current 804-1 and 804-2, the peak 610-1 of excitation isshifted away from the stimulation site associated with electrode E2, asshown in FIG. 6. This is because the compensating current 804-1 appliedto E1 is relatively closer to E2 than the compensating current 804-2applied to E4. Hence, it may be impossible for a cochlear implant systememploying a quadripolar stimulation strategy to stimulate stimulationsites located on the boundary of a stimulation channel.

Panel 602-2 also shows an exemplary excitation field 608-2 (representedby a dashed line) that may result in response to stimulation ofelectrode E3 in the presence of fixed compensating current applied toelectrodes E1 and E4. Such stimulation is illustrated in FIG. 8B. Asshown in FIG. 8B, main current 806 is applied to electrode E3 at thesame time that fixed compensating current 804-1 and 804-2 opposite inpolarity compared to main current 806 is applied to electrodes E1 andE4. No current is applied to electrode E2. Although the resultingexcitation field 608-2 is focused due to the presence of compensatingcurrent 804-1 and 804-2, the peak 610-2 of excitation is shifted awayfrom the stimulation site associated with electrode E3, as shown in FIG.6. As described above, this is because the compensating current 804-2applied to E4 is relatively closer to E2 than the compensating current804-1 applied to E1.

Panel 602-2 also shows an exemplary excitation field 608-3 (representedby a solid line) that may result in response to concurrent stimulationof electrodes E2 and E3 in the presence of fixed compensating currentapplied to electrodes E1 and E4. Such stimulation is illustrated in FIG.8C. As shown in FIG. 8C, main current 808-1 and 808-2 is applied toelectrodes E2 and E3, respectively, at the same time that fixedcompensating current 804-1 and 804-2 opposite in polarity compared tomain current 808-1 and 808-2 is applied to electrodes E1 and E4. Theresulting excitation field 608-3 is focused due to the presence ofcompensating current 804-1 and 804-2. Moreover, because of the symmetryof the stimulation, excitation field 608-3 has a peak 610-3 thatcorresponds to a stimulation site located midway in between thestimulation sites associated with electrodes E2 and E3.

Now that monopolar and quadripolar stimulation strategies have beendescribed, the benefits of a quadripolar with correction stimulationstrategy may be recognized. To illustrate, panel 602-3 shows anexemplary excitation field 612-1 (represented by a dotted line) that mayresult in response to stimulation of electrode E2 in the presence ofdynamically determined compensating current applied to electrodes E1,E3, and E4. Such stimulation is illustrated in FIG. 9A. As shown in FIG.9A, main current 902 is applied to electrode E2 at the same time thatdynamically determined compensating current 904-1, 904-2, and 904-3opposite in polarity compared to main current 902 is applied toelectrodes E1, E3, and E4, respectively. The weighted amount (i.e., theamplitude) of compensating current 904-1, 904-2, and 904-3 may bedetermined based on the desired stimulation site, which, in this case,corresponds directly to electrode E2. For example, as shown in FIG. 9A,the amount of compensating current applied to electrodes E1 and E4 isgreater than that applied to electrode E3.

As illustrated in FIG. 6, the resulting excitation field 612-1 isfocused due to the presence of compensating current 904-1, 904-2, and904-3. Advantageously, by applying compensating stimulation toelectrodes E1, E3, and E4, the peak 614-1 of excitation is at thestimulation site associated with E2 (and not shifted as it was with thequadripolar stimulation strategy).

Panel 602-3 also shows an exemplary excitation field 612-2 (representedby a dashed line) that may result in response to stimulation ofelectrode E3 in the presence of dynamically determined compensatingcurrent applied to electrodes E1, E2, and E4. Such stimulation isillustrated in FIG. 9B. As shown in FIG. 9B, main current 906 is appliedto electrode E3 at the same time that dynamically determinedcompensating current 908-1, 908-2, and 908-3 opposite in polaritycompared to main current 902 is applied to electrodes E1, E2, and E4,respectively. The weighted amount (i.e., the amplitude) of compensatingcurrent 908-1, 908-2, and 908-3 may be determined based on the desiredstimulation site, which, in this case, corresponds directly to electrodeE3. For example, as shown in FIG. 9B, the amount of compensating currentapplied to electrodes E1 and E4 is greater than that applied toelectrode E2.

As illustrated in FIG. 6, the resulting excitation field 612-2 isfocused due to the presence of compensating current 908-1, 908-2, and908-3. Advantageously, by applying compensating stimulation toelectrodes E1, E2, and E4, the peak 614-2 of excitation is at thestimulation site associated with E3 (and not shifted as it was with thequadripolar stimulation strategy).

Panel 602-3 also shows an exemplary excitation field 612-3 (representedby a solid line) that may result in response to concurrent stimulationof electrodes E2 and E3 in the presence of dynamically determinedcompensating current applied to electrodes E1 and E4. Such stimulationis illustrated in FIG. 9C. As shown in FIG. 9C, main current 910-1 and910-2 is applied to electrodes E2 and E3, respectively, at the same timethat dynamically determined compensating current 912-1 and 912-2opposite in polarity compared to main current 910-1 and 910-2 is appliedto electrodes E1 and E4. The resulting excitation field 612-3 is focuseddue to the presence of compensating current 912-1 and 912-2. Moreover,because of the symmetry of the stimulation, excitation field 612-3 has apeak 614-3 that corresponds to a stimulation site located midway inbetween the stimulation sites associated with electrodes E2 and E3.

In general, stimulation management facility 304 may use the quadripolarwith correction stimulation strategy illustrated in FIG. 6 and FIG. 9 tostimulate any stimulation site associated with the stimulation channeldefined by electrodes E2 and E3.

For example, processing facility 302 may identify a stimulation siteassociated with electrode E2 as the stimulation site that is to bestimulated in order to represent an audio signal to a patient. Inresponse, stimulation management facility 304 may dynamically designate,based on the identified stimulation site, electrode E2 as being a lonemain electrode and electrodes E1, E3, and E4 as being compensatingelectrodes. Stimulation management facility 304 may also dynamicallydetermine, based on the identified stimulation site, an amount of maincurrent to be applied to electrode E2, a first weighted amount ofcompensating current to be applied to electrode E1, a second weightedamount of compensating current to be applied to electrode E3, and athird weighted amount of compensating current to be applied to electrodeE4. Stimulation management facility 304 may then direct cochlear implant108 to stimulate the identified stimulation site by concurrentlyapplying the determined amount of main current to electrode E2 and thedetermined weighted amounts of compensating current to electrodes E1,E3, and E4.

Processing facility 302 may subsequently identify a stimulation siteassociated with electrode E3 as the stimulation site that is to bestimulated in order to represent a different audio signal to thepatient. In response, stimulation management facility 304 maydynamically designate, based on the identified stimulation site,electrode E3 as being a lone main electrode and electrodes E1, E2, andE4 as being compensating electrodes. Stimulation management facility 304may also dynamically determine, based on the identified stimulationsite, an amount of main current to be applied to electrode E3, a firstweighted amount of compensating current to be applied to electrode E1, asecond weighted amount of compensating current to be applied toelectrode E2, and a third weighted amount of compensating current to beapplied to electrode E4. Stimulation management facility 304 may thendirect cochlear implant 108 to stimulate the identified stimulation siteby concurrently applying the determined amount of main current toelectrode E3 and the determined weighted amounts of compensating currentto electrodes E1, E2, and E4.

Processing facility 302 may subsequently identify a stimulation sitelocated somewhere in between stimulation sites associated withelectrodes E2 and E3 as the stimulation site that is to be stimulated inorder to represent yet a different audio signal to the patient. Inresponse, stimulation management facility 304 may dynamically designate,based on the identified stimulation site, electrodes E2 and E3 as beingmain electrodes and electrodes E1 and E4 as being compensatingelectrodes. Stimulation management facility 304 may also dynamicallydetermine, based on the identified stimulation site, a first weightedamount of main current to be applied to electrode E2, a second weightedamount of main current to be applied to electrode E3, a first weightedamount of compensating current to be applied to electrode E1, and asecond weighted amount of compensating current to be applied toelectrode E4. Stimulation management facility 304 may then directcochlear implant 108 to stimulate the identified stimulation site byconcurrently applying the determined weighted amounts of main current toelectrodes E2 and E3 and the determined weighted amounts of compensatingcurrent to electrodes E1 and E4.

Continuing with the example in which four electrodes correspond to thestimulation channel associated with the identified stimulation site,stimulation management facility 304 may alternatively perform thedynamic designation and the dynamic determination in accordance with anarrow focused stimulation strategy. A “narrow focused stimulationstrategy” is similar to the quadripolar with correction stimulationstrategy described above, except that only two compensating electrodes(as opposed to three) are used when the identified stimulation site isassociated with a boundary of the stimulation channel.

To illustrate an exemplary narrow focused stimulation strategy,reference is made to FIG. 10. FIG. 10 includes three panels 1002-1through 1002-3 that each show excitation fields that may occur inresponse to stimulation of various configurations of four electrodeslabeled E1 through E4.

Panel 1002-1 illustrates a scenario in which processing facility 302identifies a stimulation site associated with electrode E2 as thestimulation site that is to be stimulated in order to represent an audiosignal to a patient. In response, stimulation management facility 304may dynamically designate, based on the identified stimulation site,electrode E2 as being a lone main electrode and electrodes E1 and E3 asbeing compensating electrodes. Stimulation management facility 304 mayalso dynamically determine, based on the identified stimulation site, anamount of main current 1004 to be applied to electrode E2, a firstweighted amount of compensating current 1006-1 to be applied toelectrode E1, and a second weighted amount of compensating current1006-2 to be applied to electrode E3.

Stimulation management facility 304 may then direct cochlear implant 108to stimulate the identified stimulation site by concurrently applyingthe determined amount of main current to electrode E2 and the determinedweighted amounts of compensating current to electrodes E1 and E3. Asshown, stimulation management facility 304 may direct cochlear implant108 to abstain from applying current to electrode E4. By so doing, anexcitation field 1008 generated by main current 1004 may be focused. Forthe sake of comparison, an excitation field 1010 caused by monopolarstimulation of electrode E2 in the absence of compensation current isalso shown in panel 1002-1. As shown, excitation field 1008 isrelatively more focused than excitation field 1010. In some cases, thedegree of focusing may be narrower than that achieved in the quadripolarwith correction stimulation strategy because fewer electrodes (i.e., twoversus three) are used to focus excitation field 1008.

As another example of the narrow focused stimulation strategy, panel1002-2 illustrates a scenario in which processing facility 302identifies a stimulation site located midway between the stimulationsites associated with electrodes E2 and E3 as the stimulation site thatis to be stimulated in order to represent an audio signal to a patient.In response, stimulation management facility 304 may dynamicallydesignate, based on the identified stimulation site, electrodes E2 andE3 as being main electrodes and electrodes E1 and E4 as beingcompensating electrodes. Stimulation management facility 304 may alsodynamically determine, based on the identified stimulation site, a firstweighted amount of main current 1012-1 to be applied to electrode E2, asecond weighted amount of main current 1012-2 to be applied to electrodeE3, a first weighted amount of compensating current 1014-1 to be appliedto electrode E1, and a second weighted amount of compensating current1014-2 to be applied to electrode E4.

Stimulation management facility 304 may then direct cochlear implant 108to stimulate the identified stimulation site by concurrently applyingthe determined weighted amounts of main current to electrodes E2 and E3,and the determined weighted amounts of compensating current toelectrodes E1 and E4. By so doing, an excitation field 1016 generated bymain current 1012-1 and 1012-2 may be focused. For the sake ofcomparison, an excitation field 1018 caused by conventional currentsteering between electrodes E2 and E3 in the absence of compensationcurrent is also shown in panel 1002-2. As shown, excitation field 1016is relatively more focused than excitation field 1018.

As another example of the narrow focused stimulation strategy, panel1002-3 illustrates a scenario in which processing facility 302identifies a stimulation site associated with electrode E3 as thestimulation site that is to be stimulated in order to represent an audiosignal to a patient. In response, stimulation management facility 304may dynamically designate, based on the identified stimulation site,electrode E3 as being a lone main electrode and electrodes E2 and E4 asbeing compensating electrodes. Stimulation management facility 304 mayalso dynamically determine, based on the identified stimulation site, anamount of main current 1020 to be applied to electrode E3, a firstweighted amount of compensating current 1022-1 to be applied toelectrode E2, and a second weighted amount of compensating current1022-2 to be applied to electrode E4.

Stimulation management facility 304 may then direct cochlear implant 108to stimulate the identified stimulation site by concurrently applyingthe determined amount of main current to electrode E3 and the determinedweighted amounts of compensating current to electrodes E2 and E4. Asshown, stimulation management facility 304 may direct cochlear implant108 to abstain from applying current to electrode E1. By so doing, anexcitation field 1024 generated by main current 1020 may be focused. Forthe sake of comparison, an excitation field 1026 caused by monopolarstimulation of electrode E3 in the absence of compensation current isalso shown in panel 1002-3. As shown, excitation field 1024 isrelatively more focused than excitation field 1026. In some cases, thedegree of focusing may be narrower than that achieved in the quadripolarwith correction stimulation strategy because fewer electrodes (i.e., twoversus three) are used to focus excitation field 1024.

In some examples, three electrodes correspond to the stimulation channelassociated with the identified stimulation site—a first electrode, asecond electrode, and a third electrode sequentially disposed within thecochlea. The first electrode is the most apically disposed of the threeelectrodes and the third electrode is the most basally disposed of thethree electrodes. In these examples, stimulation management facility 304may perform the dynamic designation and the dynamic determination inaccordance with an inverse steering stimulation strategy. As usedherein, an “inverse steering stimulation strategy” is one in whichstimulation management facility 304 dynamically designates, based on theidentified stimulation site, the middle electrode (i.e., the secondelectrodes) as the main electrode and one or both of the flankingelectrodes (i.e., the first and/or third electrode) as compensatingelectrodes.

To illustrate an exemplary inverse steering stimulation strategy,reference is made to FIG. 11. FIG. 11 includes three panels 1102-1through 1102-3 that each show excitation fields that may occur inresponse to stimulation of various configurations of three electrodeslabeled E1 through E3.

Panel 1102-1 illustrates a scenario in which processing facility 302identifies a stimulation site associated with electrode E3 as thestimulation site that is to be stimulated in order to represent an audiosignal to a patient. In response, stimulation management facility 304may dynamically designate, based on the identified stimulation site,electrode E2 as being a lone main electrode and electrode E1 as being alone compensating electrode. Stimulation management facility 304 mayalso dynamically determine, based on the identified stimulation site, anamount of main current 1104 to be applied to electrode E2 and an amountof compensating current 1106 to be applied to electrode E1.

Stimulation management facility 304 may then direct cochlear implant 108to stimulate the identified stimulation site by concurrently applyingthe determined amount of main current to electrode E2 and the determinedamount of compensating current to electrode E1. As shown, stimulationmanagement facility 304 may direct cochlear implant 108 to abstain fromapplying current to electrode E3. By so doing, an excitation field 1108generated by main current 1104 may be focused. For the sake ofcomparison, an excitation field 1110 caused by monopolar stimulation ofelectrode E3 in the absence of compensation current is also shown inpanel 1102-1. As shown, excitation field 1108 is relatively more focusedthan excitation field 1110.

Compensating current 1106 may also shift a peak 1112 of excitation field1108 to the right such that it is roughly located at the stimulationsite associated with electrode E3. For the sake of comparison, a peak1114 of excitation field 1110 is also indicated in panel 1102-1.

Panel 1102-2 illustrates a scenario in which processing facility 302identifies a stimulation site associated with electrode E2 as thestimulation site that is to be stimulated in order to represent an audiosignal to a patient. In response, stimulation management facility 304may dynamically designate, based on the identified stimulation site,electrode E2 as being a lone main electrode and electrodes E1 and E3 asbeing compensating electrodes. Stimulation management facility 304 mayalso dynamically determine, based on the identified stimulation site, anamount of main current 1116 to be applied to electrode E2, a firstweighted amount of compensating current 1118-1 to be applied toelectrode E1, and a second weighted amount of compensating current1118-2 to be applied to electrode E3.

Stimulation management facility 304 may then direct cochlear implant 108to stimulate the identified stimulation site by concurrently applyingthe determined amount of main current to electrode E2 and the determinedamounts of compensating current to electrodes E1 and E3. Thecompensating current 1118-1 and 1118-2 may focus an excitation field1120 generated by main current 1116. For the sake of comparison, anexcitation field 1122 caused by monopolar stimulation of electrode E2 inthe absence of compensation current is also shown in panel 1102-2. Asshown, excitation field 1120 is relatively more focused than excitationfield 1122.

Panel 1102-3 illustrates a scenario in which processing facility 302identifies a stimulation site associated with electrode E1 as thestimulation site that is to be stimulated in order to represent an audiosignal to a patient. In response, stimulation management facility 304may dynamically designate, based on the identified stimulation site,electrode E2 as being a lone main electrode and electrode E3 as being alone compensating electrode. Stimulation management facility 304 mayalso dynamically determine, based on the identified stimulation site, anamount of main current 1126 to be applied to electrode E2 and an amountof compensating current 1128 to be applied to electrode E3.

Stimulation management facility 304 may then direct cochlear implant 108to stimulate the identified stimulation site by concurrently applyingthe determined amount of main current to electrode E2 and the determinedamount of compensating current to electrode E3. As shown, stimulationmanagement facility 304 may direct cochlear implant 108 to abstain fromapplying current to electrode E1. By so doing, an excitation field 1130generated by main current 1126 may be focused. For the sake ofcomparison, an excitation field 1132 caused by monopolar stimulation ofelectrode E1 in the absence of compensation current is also shown inpanel 1102-3. As shown, excitation field 1130 is relatively more focusedthan excitation field 1132.

Compensating current 1128 may also shift a peak 1134 of excitation field1130 to the left such that it is roughly located at the stimulation siteassociated with electrode E1. For the sake of comparison, a peak 1136 ofexcitation field 1132 is also indicated in panel 1102-3.

The inverse steering stimulation strategy described herein mayadvantageously use relatively few electrodes and may result in arelatively high degree of focusing, which may be beneficial when it isdesirable to represent frequencies at or near the boundary of ananalysis channel. The inverse steering stimulation strategy describedherein may be beneficial for various other reasons. It should be notedthat in some embodiments, the choice of the stimulation configurationmay be influenced not only by energy corresponding to the channel, butalso by activity on a plurality of neighboring channels. For example, ifa relatively large spectral peak is spanning a few channels, then theoptimal configuration may be selected within each channel to representthis peak.

In some examples, once processing facility 302 has divided an audiosignal presented to a patient into a plurality of analysis channels eachcontaining a frequency domain signal representative of a distinctfrequency portion of the audio signal, stimulation management facility304 may direct cochlear implant 108 to apply electrical stimulationrepresentative of each frequency domain signal included in the pluralityof analysis channels in accordance with a stimulation strategy thatincludes a degree of focusing that is analysis channel-dependent. Such astimulation strategy may be referred to herein as an “array extensionsteering stimulation strategy.”

FIG. 12 illustrates an exemplary array extension steering stimulationstrategy 1200. In this strategy, two electrodes define each stimulationchannel. For example, electrodes E1 and E2 define a first stimulationchannel, electrodes E2 and E3 define a second stimulation channel, etc.In accordance with this stimulation strategy, current steering betweeneach electrode pair is used to represent each frequency domain signal.For example, FIG. 12 shows that during each time slot (labeled “Time” inFIG. 12), equally weighted main current having an amplitude of 0.5 isapplied to each electrode pair in a particular stimulation channel. Toillustrate, during time slot 1, equally weighted main current is appliedto electrodes E1 and E2. It will be recognized that FIG. 12 shows thatequally weighted main current is applied to both electrodes in anelectrode pair for illustrative purposes only. Different weights may beused to stimulate different stimulation sites within each stimulationchannel as may serve a particular implementation.

As shown in FIG. 12, the amount of compensating current applied tocompensating electrodes during each time slot is analysis-channeldependent. For example, for the most apical pair (i.e., electrodes E1and E2), the compensation is placed on the electrode basal to the pair(i.e., electrode E3). For the next electrode pair (i.e., electrodes E2and E3), most of the compensation current is placed on the basalelectrode (i.e., electrode E4), and some compensation current is placedon the apical electrode (i.e., electrode E1). Similarly, there is aprogression on the basal side where progressively less and lesscompensation is placed on the apical compensating electrode, and more isplaced on the basal compensating electrode. The net result may be thatbetter separation of stimulation channels is achieved across theelectrode array.

FIG. 13 illustrates an exemplary implementation 1300 of current steeringthat may be used in connection with any of the stimulation strategiesdescribed herein. The components and functions illustrated in FIG. 13may be implemented by any of the systems, facilities, and/or modulesdescribed herein. For example, one or more components of sound processor104 may be configured to perform any of the functions described inconnection with FIG. 13.

As shown in FIG. 13, current steering may be applied to two or moreelectrodes 1302 (e.g., electrodes 1302-1 and 1302-2). Two electrodes1302 are shown in FIG. 13 for illustrative purposes only. It will berecognized that current steering may alternatively be applied to threeor more electrodes as may serve a particular application. Electrodes1302-1 and 1302-2 may be adjacent one to another (i.e., no otherelectrode 1302 is physically disposed in between them on a lead).Alternatively, electrodes 1302-1 and 1302-2 may be non-adjacent (i.e.,one or more electrodes 1302 are physically disposed in between them on alead).

As shown in FIG. 13, an input signal may be filtered by at least onefilter 1304 configured to generate a frequency domain signalrepresentative of a distinct frequency portion of the audio signal. Theinput signal is also input into a frequency estimator 1306 configured toestimate the peak frequency thereof. A time pattern block 1308 isconfigured to build the temporal structure of a pulse train representingthe signal output by the at least one filter 1304. Mapping modules 1310are configured to map the amplitude of the signal output by the timepattern block 1308 to corresponding current levels in accordance with asuitable mapping function.

The output of each mapping module 1310 is input into a current steeringmodule 1312. The current steering module 1312 is also configured toreceive the output of the frequency estimator 1306. In some examples,the current steering module 1312 is configured to determine appropriateweighting factors for current to be applied to electrodes 1302-1 and1302-2. This determination may be based at least in part on the peakfrequency estimate and the output of each of the mapping modules 1310.The weighting factors may be applied to the current using multiplicationblocks 1314. In this manner, stimulation current may be delivered to astimulation site located in between areas associated with electrodes1302-1 and 1302-2.

The excitation field produced by the current steering electrodes 1302-1and 1302-2 may be focused by applying compensating currentsimultaneously to one or more additional electrodes (referred to hereinas compensating electrodes). To illustrate, FIG. 14 illustrates anotherexemplary implementation 1400 of a current steering strategy that may beused to dynamically focus one or more excitation fields produced bycurrent steering electrodes (e.g., electrodes 1302-1 and 1302-2). Thecomponents and functions illustrated in FIG. 14 may be implemented byany of the systems, facilities, and/or modules described herein. Forexample, one or more components of sound processor 104 may be configuredto perform any of the functions described in connection with FIG. 14.

Implementation 1400 includes many of the same components as theimplementation described in connection with FIG. 13. In addition,functional block diagram 1400 includes a focusing factor generator 1402configured to generate focusing factor σ based on the amplitude of thesignal output by filter 1304. The focusing factor σ is used to generatescaled versions of the current steering current. This scaled current isdelivered via one or more additional electrodes (e.g., electrodes 1302-3and 1302-4) to effectively focus or narrow the excitation field producedby electrodes 1302-1 and 1302-2.

As shown in FIG. 14, loudness compensators 1404 may also be includedwithin the implementation 1400 of FIG. 14. Loudness compensators 1404are configured to adjust the amplitudes of the currents applied viaelectrodes 1302-1 and 1302-2 to compensate for loudness changes that maybe caused by current delivered via the compensating electrodes 1302-3and 1302-4.

While exemplary implementations 1300 and 1400 of current steering havebeen described herein, it will be recognized that other implementationsof current steering may be additionally or alternatively used inconnection with the systems and methods described herein as may serve aparticular implementation.

FIG. 15 illustrates an exemplary focusing method 1500 for use in acochlear implant system. While FIG. 15 illustrates exemplary stepsaccording to one embodiment, other embodiments may omit, add to,reorder, and/or modify any of the steps shown in FIG. 15. One or more ofthe steps shown in FIG. 15 may be performed by sound processor 104and/or any implementation thereof.

In step 1502, a sound processor identifies a stimulation site within acochlea of a patient that is to be stimulated in order to represent anaudio signal presented to the patient, the stimulation site includedwithin a plurality of stimulation sites associated with a stimulationchannel corresponding to a plurality of electrodes. Step 1502 may beperformed in any of the ways described herein.

In step 1504, the sound processor dynamically designates, based on theidentified stimulation site, a first group of one or more electrodesincluded in the plurality of electrodes as a group of one or more mainelectrodes and a second group of one or more electrodes included in theplurality of electrodes as a group of one or more compensatingelectrodes. Step 1504 may be performed in any of the ways describedherein.

In step 1506, the sound processor dynamically determines, based on theidentified stimulation site, an amount of main current to be applied toeach electrode included in the first group of one or more electrodes inorder to represent the audio signal and an amount of compensatingcurrent to be applied to each electrode included in the second group ofone or more electrodes to focus an excitation field created by the maincurrent, the compensating current opposite in polarity compared to themain current. Step 1506 may be performed in any of the ways describedherein.

In the preceding description, various exemplary embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe scope of the invention as set forth in the claims that follow. Forexample, certain features of one embodiment described herein may becombined with or substituted for features of another embodimentdescribed herein. The description and drawings are accordingly to beregarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A system comprising: a processing facility thatidentifies a stimulation site within a cochlea of a patient that is tobe stimulated in order to represent an audio signal presented to thepatient, the stimulation site included within a plurality of stimulationsites associated with a stimulation channel corresponding to a pluralityof electrodes; and a stimulation management facility communicativelycoupled to the processing facility and that dynamically designates,based on the identified stimulation site, a first group of one or moreelectrodes included in the plurality of electrodes as a group of one ormore main electrodes and a second group of one or more electrodesincluded in the plurality of electrodes as a group of one or morecompensating electrodes, and dynamically determines, based on theidentified stimulation site, an amount of main current to be applied toeach electrode included in the first group of one or more electrodes inorder to represent the audio signal and an amount of compensatingcurrent to be applied to each electrode included in the second group ofone or more electrodes to focus an excitation field created by the maincurrent, the compensating current opposite in polarity compared to themain current.
 2. The system of claim 1, wherein the stimulationmanagement facility directs a cochlear implant associated with thepatient to stimulate the identified stimulation site by concurrently:applying the determined amount of main current to the first group of oneor more electrodes; and applying the determined amount of compensationcurrent to the second group of one or more electrodes.
 3. The system ofclaim 1, wherein the plurality of electrodes comprises a firstelectrode, a second electrode, a third electrode, and a fourth electrodesequentially disposed within the cochlea, and wherein the stimulationmanagement facility performs the dynamic designation and the dynamicdetermination in accordance with a quadripolar with correctionstimulation strategy.
 4. The system of claim 3, wherein: the identifiedstimulation site is in between a stimulation site associated with thesecond electrode and a stimulation site associated with the thirdelectrode; the stimulation management facility performs the dynamicdesignation in accordance with the quadripolar with correctionstimulation strategy by designating, based on the identified stimulationsite being in between the stimulation site associated with the secondelectrode and the stimulation site associated with the third electrode,the second and third electrodes as being main electrodes included in thegroup of one or more main electrodes and the first and fourth electrodesas being compensating electrodes included in the group of one or morecompensating electrodes; and the stimulation management facilityperforms the dynamic determination in accordance with the quadripolarwith correction stimulation strategy by determining, based on theidentified stimulation site being in between the stimulation siteassociated with the second electrode and the stimulation site associatedwith the third electrode, a first weighted amount of the main current tobe applied to the second electrode in accordance with a current steeringstrategy, a second weighted amount of the main current to be applied tothe third electrode in accordance with the current steering strategy, afirst weighted amount of the compensating current to be applied to thefirst electrode, and a second weighted amount of the compensatingcurrent to be applied to the fourth electrode.
 5. The system of claim 3,wherein: the identified stimulation site is associated with the secondelectrode; the stimulation management facility performs the dynamicdesignation in accordance with the quadripolar with correctionstimulation strategy by designating, based on the identified stimulationsite being associated with the second electrode, the second electrode asbeing a lone main electrode included in the group of one or more mainelectrodes and the first, third, and fourth electrodes as beingcompensating electrodes included in the group of one or morecompensating electrodes; and the stimulation management facilityperforms the dynamic determination in accordance with the quadripolarwith correction stimulation strategy by determining, based on theidentified stimulation site being associated with the second electrode,the amount of main current to be applied to the second electrode, afirst weighted amount of the compensating current to be applied to thefirst electrode, a second weighted amount of the compensating current tobe applied to the third electrode, and a third weighted amount of thecompensating current to be applied to the fourth electrode.
 6. Thesystem of claim 3, wherein: the identified stimulation site isassociated with the third electrode; the stimulation management facilityperforms the dynamic designation in accordance with the quadripolar withcorrection stimulation strategy by designating, based on the identifiedstimulation site being associated with the third electrode, the thirdelectrode as being a lone main electrode included in the group of one ormore main electrodes and the first, second, and fourth electrodes asbeing compensating electrodes included in the group of one or morecompensating electrodes; and the stimulation management facilityperforms the dynamic determination in accordance with the quadripolarwith correction stimulation strategy by determining, based on theidentified stimulation site being associated with the third electrode,the amount of main current to be applied to the third electrode, a firstweighted amount of the compensating current to be applied to the firstelectrode, a second weighted amount of the compensating current to beapplied to the second electrode, and a third weighted amount of thecompensating current to be applied to the fourth electrode.
 7. Thesystem of claim 1, wherein the plurality of electrodes comprises a firstelectrode, a second electrode, and a third electrode sequentiallydisposed within the cochlea, and wherein the stimulation managementfacility performs the dynamic designation and the dynamic determinationin accordance with an inverse steering strategy.
 8. The system of claim7, wherein: the identified stimulation site is associated with the firstelectrode; the stimulation management facility performs the dynamicdesignation in accordance with the quadripolar with correctionstimulation strategy by designating, based on the identified stimulationsite being associated with the first electrode, the second electrode asbeing a lone main electrode included in the group of one or more mainelectrodes and the third electrode as being a lone compensatingelectrode included in the group of one or more compensating electrodes;and the stimulation management facility performs the dynamicdetermination in accordance with the inverse steering strategy bydetermining, based on the identified stimulation site being associatedwith the first electrode, the amount of main current to be applied tothe second electrode, and the amount of compensating current to beapplied to the third electrode.
 9. The system of claim 8, wherein thestimulation management facility directs a cochlear implant associatedwith the patient to stimulate the identified stimulation site byconcurrently: applying the determined amount of main current to thesecond electrode; applying the determined amount of compensation currentto the third electrode; and abstaining from applying current to thefirst electrode.
 10. The system of claim 7, wherein: the identifiedstimulation site is associated with the second electrode; thestimulation management facility performs the dynamic designation inaccordance with the quadripolar with correction stimulation strategy bydesignating, based on the identified stimulation site being associatedwith the second electrode, the second electrode as being a lone mainelectrode included in the group of one or more main electrodes and thefirst and third electrodes as being compensating electrodes included inthe group of one or more compensating electrodes; and the stimulationmanagement facility performs the dynamic determination in accordancewith the inverse steering strategy by determining, based on theidentified stimulation site being associated with the second electrode,the amount of main current to be applied to the second electrode, afirst weighted amount of the compensating current to be applied to thefirst electrode, and a second weighted amount of the compensatingcurrent to be applied to the third electrode.
 11. The system of claim 7,wherein: the identified stimulation site is associated with the thirdelectrode; the stimulation management facility performs the dynamicdesignation in accordance with the quadripolar with correctionstimulation strategy by designating, based on the identified stimulationsite being associated with the third electrode, the second electrode asbeing a lone main electrode included in the group of one or more mainelectrodes and the first electrode as being a lone compensatingelectrode included in the group of one or more compensating electrodes;and the stimulation management facility performs the dynamicdetermination in accordance with the inverse steering strategy bydetermining, based on the identified stimulation site being associatedwith the first electrode, the amount of main current to be applied tothe second electrode, and the amount of compensating current to beapplied to the first electrode.
 12. The system of claim 11, wherein thestimulation management facility directs a cochlear implant associatedwith the patient to stimulate the identified stimulation site byconcurrently: applying the determined amount of main current to thesecond electrode; applying the determined amount of compensation currentto the first electrode; and abstaining from applying current to thethird electrode.
 13. The system of claim 1, wherein the plurality ofelectrodes comprises a first electrode, a second electrode, a thirdelectrode, and a fourth electrode sequentially disposed within thecochlea, and wherein the stimulation management facility performs thedynamic designation and the dynamic determination in accordance with anarrow focused steering stimulation strategy.
 14. The system of claim13, wherein: the identified stimulation site is associated with thesecond electrode; the stimulation management facility performs thedynamic designation in accordance with the narrow focused steeringstimulation strategy by designating, based on the identified stimulationsite being associated with the second electrode, the second electrode asbeing a lone main electrode included in the group of one or more mainelectrodes and the first and third electrodes as being compensatingelectrodes included in the group of one or more compensating electrodes;and the stimulation management facility performs the dynamicdetermination in accordance with the narrow focused steering stimulationstrategy by determining, based on the identified stimulation site beingassociated with the second electrode, the amount of main current to beapplied to the second electrode, a first weighted amount of thecompensating current to be applied to the first electrode, and a secondweighted amount of the compensating current to be applied to the thirdelectrode.
 15. The system of claim 14, wherein the stimulationmanagement facility directs a cochlear implant associated with thepatient to stimulate the identified stimulation site by concurrently:applying the determined amount of main current to the second electrode;applying the determined first weighted amount of the compensatingcurrent to the first electrode; applying the determined second weightedamount of the compensating current to the third electrode; andabstaining from applying current to the fourth electrode.
 16. The systemof claim 13, wherein: the identified stimulation site is associated withthe third electrode; the stimulation management facility performs thedynamic designation in accordance with the narrow focused steeringstimulation strategy by designating, based on the identified stimulationsite being associated with the third electrode, the third electrode asbeing a lone main electrode included in the group of one or more mainelectrodes and the second and fourth electrodes as being compensatingelectrodes included in the group of one or more compensating electrodes;and the stimulation management facility performs the dynamicdetermination in accordance with the narrow focused steering stimulationstrategy by determining, based on the identified stimulation site beingassociated with the third electrode, the amount of main current to beapplied to the third electrode, a first weighted amount of thecompensating current to be applied to the second electrode, and a secondweighted amount of the compensating current to be applied to the fourthelectrode.
 17. The system of claim 16, wherein the stimulationmanagement facility directs a cochlear implant associated with thepatient to stimulate the identified stimulation site by concurrently:applying the determined amount of main current to the third electrode;applying the determined first weighted amount of the compensatingcurrent to the second electrode; applying the determined second weightedamount of the compensating current to the fourth electrode; andabstaining from applying current to the first electrode.
 18. The systemof claim 1, wherein: the processing facility identifies an additionalstimulation site within the cochlea of the patient that is to bestimulated in order to represent an additional audio signal presented tothe patient, the additional stimulation site included within theplurality of stimulation sites associated with the stimulation channelcorresponding to the plurality of electrodes; and the stimulationmanagement facility dynamically designates, based on the identifiedadditional stimulation site, a third group of one or more electrodesincluded in the plurality of electrodes as a group of one or more mainelectrodes and a fourth group of one or more electrodes included in theplurality of electrodes as a group of one or more compensatingelectrodes, and dynamically determines, based on the identifiedadditional stimulation site, an amount of main current to be applied toeach electrode included in the third group of one or more electrodes inorder to represent the additional audio signal and an amount ofcompensating current to be applied to each electrode included in thefourth group of one or more electrodes to focus an excitation fieldcreated by the main current applied to the third group of one or moreelectrodes, the compensating current applied to the fourth group of oneor more electrodes opposite in polarity compared to the main currentapplied to the third group of one or more electrodes.
 19. The system ofclaim 1, wherein: the processing facility identifies an additionalstimulation site within the cochlea of the patient that is to bestimulated in order to represent an additional audio signal presented tothe patient, the additional stimulation site included within theplurality of stimulation sites associated with the stimulation channelcorresponding to the plurality of electrodes; and the stimulationmanagement facility dynamically determines, based on the identifiedadditional stimulation site, a different amount of main current to beapplied to each electrode included in the first group of one or moreelectrodes in order to represent the additional audio signal and adifferent amount of compensating current to be applied to each electrodeincluded in the second group of one or more electrodes to focus anexcitation field created by the different amount of main current, thedifferent amount of compensating current opposite in polarity comparedto the different amount of main current.
 20. The system of claim 1,wherein the processing facility identifies the stimulation site by:determining a frequency of a spectral peak associated with the audiosignal and included in an analysis channel that corresponds to thefrequency channel; and identifying a stimulation site that correspondsto the identified frequency.
 21. The system of claim 1, wherein theplurality of electrodes includes one or more electrodes that define thestimulation channel and one or more electrodes adjacent to the one ormore electrodes that define the stimulation channel.
 22. The system ofclaim 1, wherein the first group of one or more electrodes and thesecond group of one or more electrodes do not overlap.
 23. A systemcomprising: a processing facility that divides an audio signal presentedto a patient into a plurality of analysis channels each containing afrequency domain signal representative of a distinct frequency portionof the audio signal, and a stimulation management facilitycommunicatively coupled to the processing facility and that directs acochlear implant associated with the patient to apply electricalstimulation representative of each frequency domain signal included inthe plurality of analysis channels in accordance with a stimulationstrategy that includes a degree of focusing that is analysischannel-dependent.
 24. A method comprising: identifying, by a soundprocessor, a stimulation site within a cochlea of a patient that is tobe stimulated in order to represent an audio signal presented to thepatient, the stimulation site included within a plurality of stimulationsites associated with a stimulation channel corresponding to a pluralityof electrodes; dynamically designating, by the sound processor based onthe identified stimulation site, a first group of one or more electrodesincluded in the plurality of electrodes as a group of one or more mainelectrodes and a second group of one or more electrodes included in theplurality of electrodes as a group of one or more compensatingelectrodes; and dynamically determining, by the sound processor based onthe identified stimulation site, an amount of main current to be appliedto each electrode included in the first group of one or more electrodesin order to represent the audio signal and an amount of compensatingcurrent to be applied to each electrode included in the second group ofone or more electrodes to focus an excitation field created by the maincurrent, the compensating current opposite in polarity compared to themain current.
 25. The method of claim 24, further comprising directing,by the sound processor, a cochlear implant associated with the patientto stimulate the identified stimulation site by: applying the determinedamount of main current to the first group of one or more electrodes; andapplying the determined amount of compensation current to the secondgroup of one or more electrodes.